The present invention belongs in the field of technologies for compacting soil obtained by disaggregation of the soil with corresponding mixing through the addition of compacting agents under pressure (cement grout, chemical mixtures, etc.) or additives that are injected through the equipment itself.
More in particular, it refers to execution of thin panels in which the thickness is very limited in comparison with the longitudinal dimensions.
The traditional procedure, with which a prevalently mechanical mixing is carried out, exploits the rotary motion of tools capable of digging and disaggregating the soil via appendages that extend radially with respect to the axis of the tool itself. The soil thus disaggregated is mixed with a cementing mixture pumped at low pressure (1-2 MPa) through mouths made in the tubular shaft in the proximity of the blades.
The limit of the above system is the shape of the cross section, which is very far from the theoretical shape of a diaphragm, and typically solutions are adopted with a plurality of tools set alongside one another having smaller diameters so as to approach the ideal shape.
For example, the technical solution described in U.S. Pat. No. 5,275,513 is very complex both as regards the movement and as regards the possibility of application on equipment that has to support and supply these types of tools.
A further known variant of the procedure described above is to use higher pressures for the cementing mixes.
The above technique, by exploiting the combination of the mechanical action of the disaggregating members of the tool and of the hydraulic energy of the pressure jets, is distinguished by a considerable speed of execution, with considerable economic advantages, but there still remain the same limits as regards the shape of the cross section that can be obtained.
In more recent times, the mixing techniques have resorted to machines bearing a pair of wheels provided with digging/mixing teeth or appendages, of the type described in EP-1,748,110, which are set up against one another and have axes of rotation that are substantially horizontal and normal to the axis of the dig.
This new equipment, commonly referred to as “milling wheels” or simply “milling cutters”, execute, as in the case of traditional mechanical mixing, a compacted section of given depth but of a rectangular, instead of circular, shape. As in the case of the first method described, also these machines can exploit, in addition to the mechanical effect, the disaggregating effect of the hydraulic energy of the pressure jets.
Unlike systems with rotating vertical axis, in which the members for generation of the motion are located above the ground, in milling cutters the motor members are set in the part of equipment that penetrates in the ground, up against the drums or inside the drums.
The rectangular shape, obtained with said equipment, enables an extremely high performance to be achieved as compared to the circular shape of the first systems described above in so far as, when a continuous linear diaphragm wall is to be made, it is far less costly and in any case faster to set alongside one another a number of rectangular diaphragms, slightly compenetrating one another, rather than circumferences secant with respect to one another.
The thicknesses required for the diaphragms in some types of works may be relatively large as compared to the transverse dimension of digging reaching ratios close to 1:2. There also exist applications, which are the ones specific to the present invention, in which the thicknesses have to be reduced as much as possible, and in this case it could be obtained ratios of 1:5, 1:10, 1:20, etc. The ideal section would be represented by a rectangle having the major side as long as possible, and the minor side around 200-500 mm in length, i.e., just enough to ensure continuity between two adjacent rectangular diaphragms.
The current solutions and the geometrical shapes of the motor members, transmission members, and cutting members adopted up to now do not, however, enable reduction of the width of the dig to a value of less than 500-600 mm.
U.S. Pat. No. 4,694,915 describes an apparatus (milling cutter) for digging diaphragm walls constituted by two cutting wheels. Each of them is mounted on a supporting structure, which is equipped with a member for transmission of motion, positioned inside the two wheels. The wheels can be set in rotation by single or separate motor members, turning in the same direction.
The main limit of this solution is that it is unable to dig right through the thickness of the cross section as the wheels must leave space for the internal transmission or for their support. If the thickness is reduced in order to obtain a thin diaphragm wall and the digging capacity (torques and powers involved) is kept constant, it is evident that, since the internal transmission has to remain unvaried, its overall dimensions will assume an increasing incidence as the thickness of the diaphragm decreases.
Fall-back solutions known in the field of diaphragm walls of large thickness, used for removing the central area, for example adopting mobile teeth (see, for example, document No. DE 10360910), or else generating movements transverse to the milling head through the use of pivoting supporting plates (see, for example, document No. EP 1746213), which can be moved during the excavation in order to cover the entire section, will not be able to find effective application if the thicknesses are small, and in any case represent a considerable structural complication.
It is also known the Italian patent IT-1,189,612, which describes and claims an apparatus (milling cutter) for digging diaphragm walls, equipped with a plurality of milling wheels and a motor-driven rotating central tip.
Since said solution envisages a series of internal gears, it does not permit the reduction of the transverse dimensions of the diaphragm wall. Given the geometry of the kinematic chain, the motor is set transverse, and this prevents reduction of the dimensions thereof into a really compact form. If the aim is to set the motor in a vertical position, it would be necessary to complicate the transmission further by adopting an additional transmission at 90° at the expense of simplification, which is already particularly critical.
In addition, the head has the purpose of digging the part of ground comprised between the plurality of wheels present, hence only in the internal portion.
The geometry of the wheels is such to present a ratio between the diameter of the wheels and the thickness that is approximately 1:1, with consequent limits on the execution of thin panels, as in the case of the previous solution.